Halogens have for many years been used as sanitizers, disinfectants and cold chemical sterilants in a wide variety of settings and environments that require the attenuation or elimination of microorganisms that adversely affect human and animal health. Ideally, the evaluation of the sterility or safety of a particular aqueous fluid suggests that a representative sample of such fluid be actually tested for the presence, level and type of adverse or harmful microorganisms. This is, however, not always possible as such a testing methodology usually requires the use of time consuming microorganism culturing techniques or large and expensive laboratory instrumentation and equipment. A simpler technique involves a system for the determination of a safe and effective level of an anti-microorganism chemical such as a halogen in the subject fluid. Such test system should be rapid and easy to use in order to ensure that this level be achieved and maintained. This is usually done by utilizing a test kit or system which is adapted to the particular fluid or environment under scrutiny.
Of the many chemical disinfectants and cold chemical sterilants now in use in human and animal health care, by far the most common are the halogens. Even though there are some drawbacks to the use of halogens as disinfectants, the low cost and availability of such materials bring them to the forefront in the continuing battle to control harmful microorganisms in the many aqueous fluids we come into contact with in our everyday lives. In this regard, chlorine and particularly free chlorine and bromine are the chemicals of choice, especially in the recreational water area.
As indicated above, it is essential that a safe and effective level of the chemical being used as a disinfectant be maintained in the aqueous environment under consideration. This level is usually monitored by employing a test device or system which is reasonably specific for the material being used. In the case of halogens and particularly hypochlorous acid (HOCl), such materials, by their very nature, are very reactive substances and numerous test methodologies based on such reactivity have been developed over the years and sold to users as testing kits and devices. By far the most common methodology employs the use of oxidation/reduction indicator materials which change color in proportion to the concentration of halogen in the fluid being tested.
One complicating factor in the use and determination of chlorine and to some extent the other halogens in aqueous fluids resides in the fact that chlorine (in the form of hypochlorous acid) tends to react with ammonia and other nitrogenous materials to produce what is known as combined chlorine or chloramines. These materials are considered to be, at least in the case of chlorine, less effective as sanitizers or disinfectants. Hypochlorous acid is also known as free or available chlorine and after a portion of such material combines with nitrogenous substances, is known as combined chlorine.
The present invention accordingly relates to an easy to use, sensitive and effective test system for the detection of free or available halogens over a broad range of concentrations in aqueous fluids. As used herein, the term "halogen" includes chlorine, bromine and iodine when such materials are used alone or in combination with other sanitizers. The term "free" or "available" or "free available" halogen (chlorine) is defined as a measure of oxidizing capacity and is expressed in terms of the equivalent amount of elemental chlorine. The term "combined" or "combined available" chlorine is defined as chlorine which has reacted with ammonia or other nitrogenous compounds and finally the "free" and "combined available" chlorine, when present in the water, are collectively described as "total residual (available)" chlorine or simply "total" chlorine.